Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare read-only, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: it discloses the aggregate scoring model (out of 100), per-check findings, and a prioritized fix list, which tells the agent what the operation produces.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the enumeration of checks and the output shape, then the when-to-use cue. Dense but every clause earns its place; no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, so the description correctly carries the return-value burden by naming the score, per-check findings and fix list. With annotations covering safety and the schema covering params, an agent has everything needed to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, and the schema fully documents both the domain input format (URLs/emails accepted, domain part extracted) and the optional dkim_selector fallback behavior. The description adds nothing beyond the schema, so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (run every email-authentication check) and resource (a domain), then enumerates the exact check families covered and the return shape. This clearly differentiates it from narrower siblings like check_blacklists and check_record, which cover only subsets.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

"Use this first when asked whether a domain is set up correctly to send email" gives a clear entry-point trigger. It implies precedence over the narrower sibling checks but never names them, so routing vs check_record/check_blacklists is left partly to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.